1. Technical Field of the Invention
The present invention relates generally to an electromagnetic switch for use in opening or closing contacts of a motor driver for automotive engine starters.
2. Background Art
There are known electromagnetic switches for use in a motor driver for engine starters. For instance, Japanese Patent First Publication No. 3-969 discloses an electromagnetic switch which includes a pair of fixed contacts to be joined to a motor driver and a moving contact retained on an end of a plunger shaft through an insulator. The moving contact is brought by the plunger shaft into abutment with the fixed contacts to establish electric communication between the fixed contacts to actuate the motor driver.
The above switch has the moving contact installed to be rotatable relative to the insulator and, thus, encounters the drawback in that relative rotation between the moving contact and the insulator due to mechanical vibrations of the switch will result in wear of the insulator, thus requiring the need for increasing the size of the insulator enough to compensate for such wear, which leads to an increased overall length of the switch.
When the moving contact abuts the fixed contacts, it will produce a physical impact on the insulator. It is, thus, necessary for the insulator to have the mechanical strength great enough to withstand such impact. Particularly, in a case where the insulator is made of resin, it will be essential to design the strength of a weld in the insulator which usually occurs during molding thereof and is weaker in mechanical strength than a remaining part of the insulator. Specifically, it is necessary for the weld to have the strength greater enough to withstand a maximum load exerted by the moving contact on the insulator. This requires increasing the thickness of the insulator, thus resulting in an increased overall length of the switch.
International Publication No. WO 00/26533, Japanese Patent No. 3152248, and Japanese Patent First Publication No. 2003-184710 disclose the above type of electromagnetic switch.